There is used a bumper device for buffering an impact energy transmitted from a bumper reinforcement to a vehicle body as less as possible in collision of a vehicle and restraining an adverse influence on a passenger.
The bumper devices are of a type for arranging a bumper stay between a bumper reinforcement extended in a width direction of a vehicle and a side member (also referred to as side frame) on each side of a vehicle body and absorbing an impact energy mainly by plastic deformation of the bumper reinforcement and of a type of arranging a crash box in place of the bumper stay and absorbing the impact energy mainly by plastic deformation of the crash box.
A bumper device of the former type is disclosed in JP-A-2001-294106. The example uses a front wall in line with a rear wall of a bumper reinforcement and fixed thereto, a rear wall attached to a front end portion of a side member, and a bumper stay including at least two pieces of side walls for connecting the front wall and the rear wall.
The publicly-known bumper stay teaches forming a closed hollow portion by the front wall and the rear wall, forming an open hollow portion opened to a front side by making the front wall discontinuous, bringing the side wall into a hollow state, or arranging the side wall with an angle of inclination relative to the rear wall.
According to the pair of side walls of the bumper stay, the side wall on an inner side disposed on a center side of the vehicle is made to be longer than the side wall on an outer side and the front wall is made to coincide with a rear of the bumper reinforcement.
When an impact force (load) by collision of the vehicle is operated to the bumper reinforcement of the bumper device having such a bumper stay, before plastic deformation of the bumper reinforcement, a longer one, that is, the inner side of the side wall of the bumper stay is deformed to fall to the inner side and the impact force is absorbed by a remaining one of the side wall. Therefore, first, the bumper stay is crashed and next, the impact energy is started to be absorbed by the plastic deformation of the bumper reinforcement.
The crash of the bumper stay causes to break the side member by the impact energy, further, support of the bumper reinforcement is lost, the bumper reinforcement is produced with unexpected plastic deformation and an efficiency of absorbing the impact energy is reduced.
Therefore, it is a problem of the invention to be solved to resolve the above-described drawback of the prior art.